Persistent ICT malaria P.f/P.v panmalarial and HRP2 antigen reactivity after treatment of Plasmodium falciparum malaria is associated with gametocytemia and results in false-positive diagnoses of Plasmodium vivax in convalescence

A problem with rapid Plasmodium falciparum-specific antigen histidine-rich protein 2 (HRP2) detection tests for malaria is the persistence of antigen in blood after the disappearance of asexual-stage parasitemia and clinical symptoms, resulting in false-positive (FP) test results following treatment . The ICT P.f/P.v immunochromatographic test detects both HRP2 and a panmal arial antigen (PIMA) found in both P. falciparum and Plasmodium vivax, To e xamine posttreatment antigen persistence,vith this test and whether persist ent sexual-stage forms (gametocytes) are a cause of FP tests after treatmen t, we compared serial antigen test results with microscopy results from pat ients symptomatic with P. falciparum malaria in Indonesia for 28 days follo wing treatment with chloroquine (CQ; n = 66), sulfadoxine-pyrimethamine (SP ; n = 36), and artesunate plus sulfadoxine pyrimethamine (ART + SP; n = 15) , Persistent FP antigenemia following SP treatment occurred in 29% (HRP2) a nd 42% (PMA) of the patients on day 7 and in 10% (HRP2) and 23% (PMA) on da y 14, The high rates of persistent HRP2 and PMA antigenemia following CQ an d SP treatment were strongly associated with the presence of gametocytemia, with the proportion with gametocytes on day 7 posttreatment being signific antly greater in those with FP results than in those with true-negative PMA and HRP2 results, Gametocyte frequency on day 14 post-SP treatment was als o greater in those with FP PMA results. Following SP treatment, PMA persist ed longer than HRP2, giving an FP diagnosis of P, vivax in up to 16% of pat ients on day 14, with all FP P. vivax diagnoses having gametocytemia, In co ntrast, PMA was rapidly cleared following ART + SP treatment in association with rapid clearance of gametocytemia. Gametocytes appear to be an importa nt cause of persistent posttreatment panmalarial antigenemia in areas of en demicity and may also contribute in part to persistent HRP2 antigenemia fol lowing treatment.